1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
|
/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
* Copyright by the Board of Trustees of the University of Illinois. *
* All rights reserved. *
* *
* This file is part of HDF5. The full HDF5 copyright notice, including *
* terms governing use, modification, and redistribution, is contained in *
* the files COPYING and Copyright.html. COPYING can be found at the root *
* of the source code distribution tree; Copyright.html can be found at the *
* root level of an installed copy of the electronic HDF5 document set and *
* is linked from the top-level documents page. It can also be found at *
* http://hdf.ncsa.uiuc.edu/HDF5/doc/Copyright.html. If you do not have *
* access to either file, you may request a copy from hdfhelp@ncsa.uiuc.edu. *
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
/*-------------------------------------------------------------------------
*
* Created: H5checksum.c
* Aug 21 2006
* Quincey Koziol <koziol@hdfgroup.org>
*
* Purpose: Internal code for computing fletcher32 checksums
*
*-------------------------------------------------------------------------
*/
/****************/
/* Module Setup */
/****************/
/***********/
/* Headers */
/***********/
#include "H5private.h" /* Generic Functions */
/****************/
/* Local Macros */
/****************/
/* Polynomial quotient */
/* (same as the IEEE 802.3 (Ethernet) quotient) */
#define H5_CRC_QUOTIENT 0x04C11DB7
/******************/
/* Local Typedefs */
/******************/
/********************/
/* Package Typedefs */
/********************/
/********************/
/* Local Prototypes */
/********************/
/*********************/
/* Package Variables */
/*********************/
/*****************************/
/* Library Private Variables */
/*****************************/
/*******************/
/* Local Variables */
/*******************/
/* Table of CRCs of all 8-bit messages. */
static uint32_t H5_crc_table[256];
/* Flag: has the table been computed? */
static hbool_t H5_crc_table_computed = FALSE;
/*-------------------------------------------------------------------------
* Function: H5_checksum_fletcher32
*
* Purpose: This routine provides a generic, fast checksum algorithm for
* use in the library.
*
* Note: See the Wikipedia page for Fletcher's checksum:
* http://en.wikipedia.org/wiki/Fletcher%27s_checksum
* for more details, etc.
*
* Note #2: Per the information in RFC 3309:
* (http://tools.ietf.org/html/rfc3309)
* Fletcher's checksum is not reliable for small buffers.
*
* Note #3: The algorithm below differs from that given in the Wikipedia
* page by copying the data into 'sum1' in a more portable way
* and also by initializing 'sum1' and 'sum2' to 0 instead of
* 0xffff (for backward compatibility reasons, mostly).
*
* Return: 32-bit fletcher checksum of input buffer (can't fail)
*
* Programmer: Quincey Koziol
* Monday, August 21, 2006
*
*-------------------------------------------------------------------------
*/
uint32_t
H5_checksum_fletcher32(const void *_data, size_t _len)
{
const uint8_t *data = (const uint8_t *)_data; /* Pointer to the data to be summed */
size_t len = _len / 2; /* Length in 16-bit words */
uint32_t sum1 = 0, sum2 = 0;
FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5_checksum_fletcher32)
/* Sanity check */
HDassert(_data);
HDassert(_len > 0);
/* Compute checksum for pairs of bytes */
/* (the magic "360" value is is the largest number of sums that can be
* performed without numeric overflow)
*/
while (len) {
unsigned tlen = len > 360 ? 360 : len;
len -= tlen;
do {
sum1 += (((uint16_t)data[0]) << 8) | ((uint16_t)data[1]);
data += 2;
sum2 += sum1;
} while (--tlen);
sum1 = (sum1 & 0xffff) + (sum1 >> 16);
sum2 = (sum2 & 0xffff) + (sum2 >> 16);
}
/* Check for odd # of bytes */
if(_len % 2) {
sum1 += ((uint16_t)*data) << 8;
sum2 += sum1;
sum1 = (sum1 & 0xffff) + (sum1 >> 16);
sum2 = (sum2 & 0xffff) + (sum2 >> 16);
} /* end if */
/* Second reduction step to reduce sums to 16 bits */
sum1 = (sum1 & 0xffff) + (sum1 >> 16);
sum2 = (sum2 & 0xffff) + (sum2 >> 16);
FUNC_LEAVE_NOAPI((sum2 << 16) | sum1)
} /* end H5_checksum_fletcher32() */
/*-------------------------------------------------------------------------
* Function: H5_checksum_crc_make_table
*
* Purpose: Compute the CRC table for the CRC checksum algorithm
*
* Return: none
*
* Programmer: Quincey Koziol
* Tuesday, September 5, 2006
*
*-------------------------------------------------------------------------
*/
static void
H5_checksum_crc_make_table(void)
{
uint32_t c; /* Checksum for each byte value */
unsigned n, k; /* Local index variables */
FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5_checksum_crc_make_table)
/* Compute the checksum for each possible byte value */
for(n = 0; n < 256; n++) {
c = (uint32_t) n;
for(k = 0; k < 8; k++)
if(c & 1)
c = H5_CRC_QUOTIENT ^ (c >> 1);
else
c = c >> 1;
H5_crc_table[n] = c;
}
H5_crc_table_computed = TRUE;
FUNC_LEAVE_NOAPI_VOID
} /* end H5_checksum_crc_make_table() */
/*-------------------------------------------------------------------------
* Function: H5_checksum_crc_make_table
*
* Purpose: Update a running CRC with the bytes buf[0..len-1]--the CRC
* should be initialized to all 1's, and the transmitted value
* is the 1's complement of the final running CRC (see the
* H5_checksum_crc() routine below)).
*
* Return: 32-bit CRC checksum of input buffer (can't fail)
*
* Programmer: Quincey Koziol
* Tuesday, September 5, 2006
*
*-------------------------------------------------------------------------
*/
static uint32_t
H5_checksum_crc_update(uint32_t crc, const uint8_t *buf, size_t len)
{
size_t n; /* Local index variable */
FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5_checksum_crc_update)
/* Initialize the CRC table if necessary */
if(!H5_crc_table_computed)
H5_checksum_crc_make_table();
/* Update the CRC with the results from this buffer */
for(n = 0; n < len; n++)
crc = H5_crc_table[(crc ^ buf[n]) & 0xff] ^ (crc >> 8);
FUNC_LEAVE_NOAPI(crc)
} /* end H5_checksum_crc_update() */
/*-------------------------------------------------------------------------
* Function: H5_checksum_crc
*
* Purpose: This routine provides a generic checksum algorithm for
* use in the library.
*
* Note: This algorithm was based on the implementation described
* in the document describing the PNG image format:
* http://www.w3.org/TR/PNG/#D-CRCAppendix
*
* Return: 32-bit CRC checksum of input buffer (can't fail)
*
* Programmer: Quincey Koziol
* Tuesday, September 5, 2006
*
*-------------------------------------------------------------------------
*/
uint32_t
H5_checksum_crc(const void *_data, size_t len)
{
FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5_checksum_crc)
/* Sanity check */
HDassert(_data);
HDassert(len > 0);
FUNC_LEAVE_NOAPI(H5_checksum_crc_update((uint32_t)0xffffffffL, (const uint8_t *)_data, len) ^ 0xffffffffL)
} /* end H5_checksum_crc() */
/*-------------------------------------------------------------------------
* Function: H5_checksum_metadata
*
* Purpose: Provide a more abstract routine for checksumming metadata
* in a file, where the policy of which algorithm to choose
* is centralized.
*
* Return: checksum of input buffer (can't fail)
*
* Programmer: Quincey Koziol
* Tuesday, August 22, 2006
*
*-------------------------------------------------------------------------
*/
uint32_t
H5_checksum_metadata(const void *data, size_t len)
{
uint32_t chksum; /* Checksum value to return */
FUNC_ENTER_NOAPI_NOINIT_NOFUNC(H5_checksum_metadata)
/* Sanity check */
HDassert(data);
HDassert(len > 0);
/* Choose the appropriate checksum routine */
/* (use Fletcher's checksum for "larger" buffers and CRC for "shorter" ones) */
if(len < 256)
chksum = H5_checksum_crc(data, len);
else
chksum = H5_checksum_fletcher32(data, len);
FUNC_LEAVE_NOAPI(chksum)
} /* end H5_checksum_metadata() */
|
